1. Freezing point of Aluminium at LPM Laboratory for Process Measurement (LPM) Faculty of Mechanical Engineering and Naval Architecture, University of Zagreb, Croatia Davor Zvizdic, Tomislav Veliki

2. CONTENTS 1. Introduction 2. The apparatus for FP-Al at LPM 3. A cases of broken well and cracked tube 4. Repair, results and conclusion

3. INTRODUCTION Laboratory for Process Measurement LPM is responsible for the realization, establishment, maintenance of the: national temperature standard and National pressure standard. LPM transfers traceability to lower level standards serving the requirements of National Accreditation Service, of testing, calibration, scientific, and research laboratories and of manufacturing activities

4. LPM Laboratory for Process Measurement Realisation of ITS-90 Calibration Transfer of traceability To calibration labs, testing labs, research institututions, etc. DKD (EA/DAR/DKD) Accreditation NMI (PTB, IMGC, LNE/INM, NPL,) Bilatral intercomparisons EUROMET intercomparisons TC-Q Confidence

5. The apparatus for FP-Al at LPM Points from 8 to 17 (bolded) are currently in use in the range from -40°C to 1100°C.

6. Open cells are either of Isotech or CNAM design. Cross section of Isotech-designed fixed point used for used for Tin, Zinc, Aluminum, Silver, and Copper fixed points: A- Quartz well and crucible, B-Large graphite cell, C-graphite base, D-graphite thermometer well, E-graphite heat shunt, F-graphite washers G-graphite spacers, H-platinum foil discs, I-cap, collar and gasket assembly. Height of cell is app. 600 mm.

9. Abs. pressure gauge Vacuum pump Furnaces Pressure reg. 5.9 Argon

11. 2 blocks of 4=8 fixed point stations (ports) At any port at the same time : plateaou realisations, filling of the new cells, storing of the presurized cells, Welded SS tubing, flexible vacuum tubing and KF vacuum connectors. 3-stage membrane vacuum pump for rinsing of the cells. Presently manual argon pressure maintenance – to be automated (safety valve?). Cold trap for argon presently not used.

12. A case of well broken well At the start of FP-Al plateaou the ceramic cold rod was inserted into the cell. Upon the extraction of the rod some resistance to the upward movement of the rod was felt. Following the extraction the argon pressure was adjusted to 1013 mbar. It was immediately noticed that the cell pressure climbed to 1020 mbar which happened to be the atmospheric pressure at the moment. The leak was suspected, the furnace was shut down and the cell left to cool. The cell was diassembled and it was discoverd that the tip of the quartz re-entrant well was broken.

14. The inside of the graphyte well was inspected with the endoscopic equipment. Only relatively scarce light patches of oxydation were noticed on the inside of the well. No real pitting was found on the graphyte surface. The cell was re-assembled with the new quartz tube. The repaired cell performed well and was even used for EUROMET intercomparison.

16. A case of cracked tube (FP-Cu) Tube exchanged, assembled, rinsed, no sign of damage! Cracked at 1050 °C (sound!) Immediately rinsed with Ar Pulled out of furnace while being rinsed wiith Argon

17. CONCLUSION Open, pressure contrpolled cells, provide direct realisation of ITS-90 with known pressure at the time of realisation. Open cells allow for non-invasive, interchange of cell parts during their use. In case of adverse events (cracks in quartz parts, failure in the sedaling system, etc.):  Preventive actions can be taken to diminish possible consequences (immediate rinsing with argon, overpressure, etc.)  After the cooling the cell can be diassebled for inspection  The damaged or suspicious parts can be replaced,  The cell can be assebled in the laboratory. again in situ The re-assemled FP-Al cell showed good performance.

18. Laboratory for Process Measurement (LPM) Faculty of Mechanical Engineering and Naval Architecture University of Zagreb Ivana Lucica 5, 10000 Zagreb, Croatia tel: + 385 1 61 68 333, fax: + 385 1 61 18 714 lpm@fsb.hrlpm@fsb.hr, www.lpm.fsb.hrwww.lpm.fsb.hr Thank you for your attention!